The Herakles was a battlecruiser in service to the Dominion Fleet. After the Battle of Char, its crew sided with Valerian Mengsk in the conflict that broke out between his forces and those loyal to Arcturus Mengsk.
As the battle progressed, the ship took damage, but responded to Valerian's order to meet at designated point of clear space within the Char system. The Herakles succeeded, and entered warp space with the rest of Valerian's fleet. Unfortunately, the Dominion Fleet gave chase and the ship took more damage. It reported that it was unlikely to be able to make another jump to warp space without effecting repairs first. Still, it made the jump alongside the Bucephalus and Hyperion—all that remained of Valerian's fleet by this point. Also by this point, its crew had suffered heavy casualties.
In the interlude that followed, the crews of the Hyperion and Bucephalus searched for bugs that were allowing Arcturus to trace their position. In this time period, the Herakles's crew was transferred to the two ships. Soon enough, the Dominion Fleet arrived. As per a plan devised by Matt Horner, Captain Roger Merriman, speaking from Valerian's personal suite, gave the impression of a suicide run, sending the ship on a collision course with the White Star. While suicide wasn't on the cards, the run itself was genuine (as the ship was being guided by its adjutant) and the Herakles collided into Arcturus's flagship, doing great damage.
Herakles is a hero in Greek mythology.